The present invention relates to a method and an apparatus for quadrature detection and an MRI (Magnetic Resonance Imaging) system. More particularly, the present invention relates to a method and an apparatus for quadrature detection wherein high-frequency input signals are converted into low-frequency signals and an MRI system equipped with such a quadrature detector.
An MRI system subjects a magnetic resonance signal, received as RF (Radio Frequency) signal, to quadrature detection by reference signals to obtain a baseband signal. Then, based on the baseband signal, the MRI system reconstructs an image. In quadrature detection, in addition to the baseband signal, a signal having a center frequency two times that of the reference signals. Since this signal is unnecessary, however, it is removed through a filter. (Refer to Non-Patent Document 1, for example.)
[Non-patent Document 1] NMR Medicine, Basic and Clinical, ed. Society for the Study of Nuclear Magnetic Resonance Medicine (3rd ed.), Maruzen, Nov. 20, 1987, pp. 106–108
The frequency of the reference signal is brought into correspondence with the center frequency of the RF signal. Therefore, if the center frequency of the RF signal varies, the frequency of the reference signal must be accordingly varied. As a result, the filter for unnecessary component removal must be changed.